1. Field of the Invention
The present invention relates to coke oven batteries, particularly to slot-type oven coke oven batteries, and specifically to the design and arrangement of the sole flues in batteries which incorporate high slot-type ovens, extending in height to twenty feet or more.
2. Description of the Prior Art
The sole flues of a coke oven battery are open passages, located beneath each regenerator, through which combustion air is fed from the sides of the battery to the bottom of the regenerator chambers. The sole flues also collect the waste products of combustion from the bottom of the regenerators and conduct these gases to the sides of the battery where they are carried away in the waste heat flues.
The sole flue is a long, open, rectangular manifold, usually open on one end and closed on the other. The top of the sole flue is provided with a series of openings which control the flow of air from the sole flue into the bottom of the regenerator, and the flow of waste gases from the bottom of the regenerator into the sole flue. The air that flows through the sole flue into the regenerator is relatively cold while the waste gases that flow from the regenerator into the sole flue are in the range of the operating temperature of the coke oven battery. The air flows through a given sole flue on the "up" or burning cycle. After about a half hour, the flow is reversed, the air flow is cut off and waste gases are conducted from the regenerator into the sole flue. These two alternate flow patterns form a cycle. After the waste gas has flowed through the sole flue for about a half hour, the flow is reversed and the cycle is repeated. In the "up" cycle, blast furnace gas or "lean gas" may be added to the air to reduce the amount of coke oven gas required for the combustion that occurs above the regenerators between the oven chambers.
When the flow patterns are reversed, one to the other, there is a very rapid increase or decrease in the temperature in the sole flue producing a "thermal shock" to the refractory material from which the sole flue is constructed. This thermal shock tends to rapidly deteriorate the normal refractory materials. Thus, clay sole flue liners are used to protect the other refractory materials from this thermal shock.
Coke oven battery designs, recently, have increased in size, from the older standard height of about twelve feet to a height of twenty feet or more. To operate these tall batteries, larger burner chambers, burners and regenerators are required. This has necessitated larger volume sole flues. Since the width of the coke ovens has not varied, the underworks, including the regenerators and sole flues cannot be varied much in width. Therefore the height of both has been increased. An increase in sole flue volume is also necessitated by the use of lean gas, because sufficient air for combustion still must be introduced in addition to the lean gas that is flowed through the sole flue to the regenerators. And, as suggested before, such lean gas usage also dictates an increase in the sole flue height.
Sole flues are usually rectangular in cross section, and quite long in length vis-a-vis the cross-sectional dimensions. For example, a sole flue might be 131/8" wide.times.311/4" high.times.50' long, forming a chamber of those dimensions. The chamber is lined with clay liners in the form of flat rectangular plates. Because of structural limitations in the clay material, the plates cannot be stacked, end to end, to achieve height. Therefore, the height of the side liners needs to be generally equivalent to the height of the chamber plus some overlap to mate the sides with the bottoms. The bottom liners are between 2" and 3" thick, thus the side liners, in the dimensional example stated, need to be 331/4" to 341/4" in height to achieve a chamber height of 311/4", the design height required for a twenty foot oven.
In the field of manufacturing refractories for industrial use, the largest commonly available equipment, a Boyd "Y" press, will produce a refractory with a maximum length of 36". However, refractory shapes of maximum length are not made without difficulty; it is difficult to fill the corners of the molds when they are extended to maximum limits. This often results in missing corners and/or poorly bonded material at the corners.
The 36" maximum length which can be produced by the Boyd "Y" press is the length of the slope in the green, or unfired state. In the case of the clay liners used for sole flues, the shrinkage, due to firing, reduces the molded shape from 36" to 341/4". However, the dimensions of the shapes after firing are not uniform. There is a requirement that the liners have parallel sides and square corners to permit them to be fitted together without undue leakage. Thus, to achieve these characteristics, the refractory manufacturers must grind the edges of the shapes after firing. This grinding operation requires the removal of substantial refractory material to achieve the parallel sides and square corners. Because of the substantial warpage incurred when the green liner shapes are fired, many times the grinding required, to produce parallel sides and square corners, reduces the shape to less than the required dimension, thus making that shape unusable, i.e., it must be scrapped.
Another problem has developed from the inherent warpage which results from the firing of the clay liner shapes. Due to the flow characteristics that are required in the sole flue, the liners must have no more than a 3/16" tolerance on the flat face surfaces. The warpage that results from firing exceeds this limitation in a substantial number of cases because the overall large size of the shapes. These flat surfaces cannot be economically ground. Therefore, the shapes which are warped more than 3/16" must be scrapped.
Because of the problems of warpage, and of corner formation, the overall scrap rate in producing the clay liners has been in the 90 percentile range, rendering the cost of the acceptable shapes prohibitive.
In the design of sole flues, the top section, or the "rider tile", are supported by the side clay liners. Due to the relatively extreme height of the clay liners, required for the tall ones, the structural integrity of those tile is reduced. The cause of this reduction in structural integrity appears to be the compounding of internal stresses over a larger cross-sectional area as develops when the clay liners are subjected to the phenomena of thermal shock, as explained before. Thus, there is a proportional increase in the incidence of sole flue collapse that is directly related to the height of the clay liners.
In retrospect, the clay liners for the tall ovens are extremely expensive to manufacture due to the high scrap rates. Thus there is a need to establish a sole flue design which does not utilize the large clay liners, to enable economical manufacturing techniques to be utilized. In addition there is a need to establish a sole flue design which enhances the structural integrity of the clay liners in operation, thus providing a greater resistance to the devastating effects of thermal shock.